Liquid crystal display device

ABSTRACT

To reduce an optical leakage and a disclination. In a liquid crystal display device for a gate line inversion drive, of the end portion of a pixel electrode, the portions formed along a scanning line are raised with respect to the main face of the pixel electrode. Of the end portions of a pixel electrode, the portions formed along a signal line are formed to have a height identical to that of the main face of the pixel electrode.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device including acircuit composed of field effect transistors (FET) such as thin filmtransistors (TFT), and to a method for manufacturing the semiconductordevice. The TFT means a semiconductor element including a semiconductorlayer, a gate electrode, a source electrode and a drain electrode.

Here, the “element substrate” generally indicates the substrate having asemiconductor element such as the TFT.

Here, the “display device” generally indicates the device for displayingthe brightness with the change in an electric signal, and the displaydevice for displaying by applying the electric signal to a liquidcrystal.

2. Related Art

In recent years, there has been noted a technique for constructing theTFT by using a semiconductor thin film (having a thickness of aboutseveral to several hundreds nm) formed over a substrate having aninsulating surface. The TFT is widely applied to an electronic devicesuch as an IC or a semiconductor device and is urgently demanded for adevelopment as the switching element of the liquid crystal displaydevice.

This liquid crystal display device is coarsely divided into two knownkinds: the active matrix type and the passive matrix type. The liquidcrystal display device of the active matrix type uses the TFT as theswitching element and can achieve an image of a high quality. Thegeneral application of the active matrix type is a note-type personalcomputer but is expected as a home TV set or a mobile terminal.

Of the liquid crystal display device of the active matrix type, a liquidcrystal display device of a projection type is enabled to achieve alarge screen display by enlarging the frame to a screen. In theprojection type liquid crystal display device of recent years, there hasbeen developed the technique for making the liquid crystal displaydevice mobile by reducing the size of the liquid crystal panel to reducethe size of the optical system. With this size reduction in the opticalsystem, the cost for the optical system can be lowered to provide theliquid crystal display device at a reasonable cost.

Here, it is customary to subject the active matrix type liquid crystaldisplay device to line inversion drives. Of these line inversion drives,the source line inversion drive is made such that the polarities ofsignal voltages to be written in pixel TFTs connected with m-columns ofsignal lines are different between the adjoining signal lines, as shownin a top plan view of the pixel portion of FIG. 30. For odd frames (FIG.30A) and even frames (FIG. 30B), moreover, there are changed thepolarities of the signal voltages to be written in the pixel TFTsconnected with signal lines. The liquid crystals are prevented fromburning by changing the polarities of the signal voltages to be writtenin the pixel TFTs thereby to drive the liquid crystal with an ACcurrent. The gate line inversion drive may be effected by replacing thesignal lines of FIG. 30 by scanning lines.

An object of the present invention is to provide an active matrix typeliquid crystal display device and an element structure which is enabledto prevent an optical leakage and a disclination by examining theprinciple of the disclination and the optical leakage of a liquidcrystal systematically.

In the interface of an alignment film, the liquid crystal is oriented toraise its one end. The “pre-tilt direction” will be termed as thepositive projection of the direction, as extended from one end of theliquid crystal molecule the closest to the interface of the alignmentfilm to the other end raised from the alignment film, upon the substrateface. Moreover, the “pre-tilt angle” will be termed as the angle madebetween the interface of the alignment film and the longer axis of theliquid crystal near the interface of the alignment film. The pre-tiltangle is given by a rubbing treatment or by applying an electric fieldto the liquid crystal to switch the liquid crystal near the interface ofthe alignment film.

Moreover, the orientation failure, as caused by the fact that thedirection of the pre-tilt of the near liquid crystal is generallyopposed in the alignment film interface, will be called the“disclination”. On the other hand, there is a region where the pre-tiltangle is locally different due to the electric field distribution or theheterogeneous rubbing although the pre-tilt direction of the liquidcrystal is identical. The orientation failure, as thus caused when theorientation state is not normal, is that the brightness is locally sohigh when two polarization plates are arranged on the liquid crystalpanel that the light looks as if it leaks. Therefore, the orientation ofthe liquid crystal, in which the direction of the pre-tilt is identicalbut the pre-tilt angle is locally different, will be called the “opticalleakage”.

When the liquid crystal display device is driven by the active matrixtype, the display quality is degraded by the optical leakage and thedisclination. In other words, in the normally white mode, a shieldingfilm is required for shielding the optical leakage and the disclinationso that the aperture ratio decreases.

In the liquid crystal display device having fine pixels as in theprojection type liquid crystal display device, the disclination and theoptical leakages, if any, will take an innegligible ratio in the pixels.If the optical leakage and the disclination cannot be shielded due tothe misalignment of the shielding film, moreover, they are visuallyrecognized like bright lines, when displayed in black, to lower thecontrast. In short, it is important for the projection type liquidcrystal display device how the optical leakage and the disclination areto be suppressed.

As compared with the semantic liquid crystal having a layer structureand accordingly a high orientation order, the nematic liquid crystal iseasily subjected to the disclination and the optical leakage by theelectric field established between pixel electrodes. Especially in theorientation system using the nematic liquid crystal, therefore,countermeasures are required for reducing the disclination and theoptical leakage.

The reason why the optical leakage and the disclination occur will bedescribed with reference to a schematic diagram presenting a section ofthe pixel portion of a liquid crystal display device of FIG. 12. In theadjoining pixel electrodes of FIG. 12, it is assumed that a pixelelectrode 101 a has a potential of +5 V whereas a pixel electrode 101 bhas a potential of −5 V. An opposed electrode 102 is assumed to have apotential of 0 V. In a region where equipotential lines 103 are formedin parallel with the surfaces of the pixel electrodes, the positive typeliquid crystals are arranged such that their molecules 108 are normal attheir longer axes to the surfaces of the pixel electrodes. At the endsof the pixel electrodes, however, the equipotential lines curve so thatliquid crystal molecules 106 are oriented obliquely with respect to thesurfaces of the pixel electrodes to cause the orientation failure. It isconsidered important for reducing the orientation failure how much thecurvatures of the equipotential lines at the ends of the pixelelectrodes are reduced.

At the ends of the pixel electrodes, there are formed regions 104 of theoptical leakage in which the pre-tilt angle is locally different. Thisis because the equipotential lines curve at the end portions of thepixel electrodes so that the liquid crystal molecules 106 cannot be soswitched at the end portions of the pixel electrodes as to have theirlonger axes normal to the surfaces of the pixel electrodes.

Moreover, there is formed a region where the pre-tilt direction of theliquid crystals is reversed by the electric field at the ends of thepixel electrodes from the pre-tilt direction determined by a rubbingdirection 107. Then, the pre-tilt angle and the pre-tilt direction ofthe alignment film interface are locally abruptly changed to enlarge theorientation strain of the liquid crystals thereby to form regions 105where the disclination occurs.

It is understood that the disclination and the optical leakage arecaused from one reason that the equipotential lines parallel to thesurfaces of the pixel electrodes curve at the end portions of the pixelelectrodes. The present invention to be described in the following is sostructurally devised that the curvatures of the equipotential lines aresuppressed as much as possible and that the equipotential lines curve,if so, as close to the ends of the pixel electrodes as possible.

In order to solve the problems thus far described, there have beenadopted the following means. The end portions of the pixel electrodesare classified into band-shaped first, second, third and fourth endportions. In the pixel electrode, moreover, the flat face, as enclosedby the first end portion, the second end portion, the third end portionand the fourth end portion, will be called the “main face” of the pixelelectrode. Here, the end portion of the pixel electrode includes theends of the pixel electrode, i.e., the portions extending in a bandshape by several μm from the ends of the pixel electrode. The main faceof the pixel electrode is a flat face occupying 20% or more, preferably50% or more of the area of the pixel electrode. In short, the flat faceoccupying the maximum area of the pixel electrode is the main face ofthe pixel electrode.

One example of the pixel of the present invention will be described withreference to the top plan view of the pixel portion of the liquidcrystal display device of FIG. 2. Of the end portions of a first pixelelectrode 208 of the liquid-crystal display device for the gate lineinversion drive, a first end portion 201 of the pixel electrode isextended along a first scanning line 207A. A third end portion 203opposed to the first end portion 201 of the first pixel electrode isextended along a second scanning line 207B adjoining the first scanningline. A second end portion 202 is extended along a first signal line212A. A fourth end portion 204 is extended along a second signal line212B. The second signal line 212B is adjacent to the first signal line212A. The two end portions 206A and 206B of the first end portion areextended at their one side along the first signal line 212A and thesecond signal line 212B, respectively. The two end portions 205A and205B of the third end portion are extended at their one side along thefirst signal line 212A and the second signal line 212B, respectively.

The pixel electrodes adjoining first end portion 201 and the third endportion 203 are at the potential of polarity different from that of thefirst end portion and the third end portion. The pixel electrodesadjoining second end portion 202 and the fourth end portion 204 are atthe potential of polarity identical to that of the first end portion andthe third end portion. With reference to FIG. 2, in the liquid crystaldisplay device for the gate line inversion drive, there is a secondpixel electrode 209 which adjoins the first pixel electrode 208 acrossthe first scanning line 207A. Then, there adjoin the first end portion201 of the first pixel electrode 208 and the third end portion 203 ofthe second pixel electrode 209. At the pixel electrodes adjoining eachother across the scanning line, between the first end portion of thefirst pixel electrode and the third end portion of the second pixelelectrode, there is established an electric field as a result that thepixel electrodes having the potentials of different polarities adjoineach other.

In the liquid crystal display device for the source line inversiondrive, it is sufficient to replace the first scanning line 207A of FIG.2 by the first signal line and the second scanning line 207B by thesecond signal line. It is naturally necessary to replace the firstsignal line 212A by the first scanning line and the second signal line212B by the second scanning line. In other words, the liquid crystaldisplay device for the source line inversion drive, too, it is notdifferent from the liquid crystal display device for the gate lineinversion drive that the electric field is established between the firstend portion of the first pixel electrode and the third end portion ofthe second pixel electrode as a result that the pixel electrodes ofdifferent polarities adjoin each other.

It can be thought that the optical leakage and the disclination can bereduced by suppressing the curvatures of the equipotential lines to beformed at the ends of the pixel electrodes. However, the degree ofcurvatures of the equipotential lines at the pixel electrode endportions changes depending upon whether the adjoining pixel electrodesare at identical or different polarities. Considering whether theadjoining pixel electrodes are at identical or different polarities,therefore, the countermeasures have been made for the following cases(1) and (2) by predicting it necessary to propose a structure forsuppressing the curvatures of the equipotential lines.

[Ridges of Pixel Electrode End Portions]

(1) Adjoining Pixel Electrodes at Different Polarities

It has been simulated how the orientation of the liquid crystal ischanged by disposing the first end portion and the third end portion ofthe pixel electrode at a level close to the opposed electrode withrespect to the main face of the pixel electrode. This simulation modelis shown in FIG. 3. The simulation model of FIG. 3 presents a section ofthe pixel portion of the liquid crystal display device. The cell gap (d)indicates the distance from the surface of the opposed electrode to themain face of the pixel electrode. The distance (s) between the pixelelectrodes indicates the distance, which is measured for the pixelelectrodes adjoining in the direction parallel to the row direction ofthe display region from the end point of the pixel electrode to the endof the adjoining pixel electrode in the drawing, as formed by projectingthe shape of the adjoining pixel electrodes positively on a planecontacting with the main face of the pixel electrode. For the pixelelectrodes adjoining in the column direction, the distance is measuredin the direction parallel to the column direction of the display regionfrom the end point of the pixel electrode to the end point of theadjoining pixel electrode. The distance between the pixel electrodes maybe locally different but is represented by the distance sharing themaximum ratio in the distribution of the distances between the pixelelectrodes. If the liquid crystal display device for the gate lineinversion drive is assumed, the distance between the pixel electrodes inthe present simulation is the distance (s) between the first pixelelectrode 208 and the second pixel electrode 209 in the top plan view ofFIG. 2.

In FIG. 3, the individual electrodes have the following potentials: afirst pixel electrode 303 a at +5 V; a second pixel electrode 303 b at−5 V; and an opposed electrode 301 at 0 V. A liquid crystal 302 isexemplified by ZLI4792 made by MERK Company, and has a pre-tilt angle of6.0 degrees, a sinistrous chiral pitch of 70 μm and a twist angle of 90degrees. The pixel pitch (p) is 18 μm. The distance (s) between thefirst pixel electrode and the second pixel electrode is 2.0 μm. The cellgap (d) is 4.5 μm. It is assumed that the pixel electrode and theopposed electrode are formed over a transparent substrate 307. Thestructure is made by repeating the units of the simulation model of FIG.3 periodically. In FIG. 3, there are shown rubbing directions 305 and306. The simulation software used was LCD Master of SHINTEC Company.

Moreover, the simulation was done by using the presence and absence of aridge 304 and the width (L₁) of the first end portion as parameters. Thefirst end portion and the third end portion are formed to rise from theflat face. The overlapping widths between the ridge and the pixelelectrode, i.e., the width (L₁) of the first end portion and the width(L₂) of the third end portion are the shortest length from each point ofthe end of the pixel electrode to the side opposed to that point, in apolygon which is formed by projecting the portions raised from the mainface of the pixel electrode, positively on the face to contact with themain face of the pixel electrode. Here in the construction having theend portions of the pixel electrode on the ridge, the height of thefirst end portion is the distance between the face to contact with themain face of the pixel electrode and the uppermost end portion of thefirst end portion. The height of the third end portion is the distancebetween the face to contact with the main face of the pixel electrodeand the uppermost end portion of the third end portion. The heights (h)of the first end portion and the third end portion are set to 0.5 μm inthe simulation. In this simulation, the width (L₁) of the first endportion and the width (L₂) of the third end portion are equalized.Moreover, the heights (h) of the first end portion and the third endportion are also equalized.

Under the conditions of the simulations, there adjoin the first pixelelectrode 303 a and the second pixel electrode 303 b which havepotentials of polarities different from each other. In the liquidcrystal display device for the gate line inversion drive, specifically,the model of FIG. 3 indicates that the first pixel electrode 303 a andthe second pixel electrode 303 b adjoining the former in the columndirection have the potentials of polarities different from each other,and that a first end portion 1001 of the first pixel electrode and athird end portion 1002 of the second pixel electrode adjoin each other.

In the liquid crystal display device for the source line inversiondrive, specifically, the model indicates that the first pixel electrode303 a and the second pixel electrode 303 b adjoining the former in therow direction have the potentials of polarities different from eachother, and that the first end portion 1001 of the first pixel electrodeand the third end portion 1002 of the second pixel electrode adjoin eachother.

The results of the representative simulations presenting thecharacteristics are shown in FIG. 13 and FIG. 14. FIG. 13 and FIG. 14present relations between the width and transmittance of the pixelelectrode overlapping the ridge. FIG. 13A shows the case in which thepixel electrode is formed on the flat face; FIG. 13B shows the case inwhich the ends (i.e., the first end portion and the third end portion)of the pixel electrode are formed over the ridge by 1.4 μm; and FIG. 14shows the case in which the ends (i.e., the first end portion and thethird end portion) of the pixel electrode are formed over the ridge by4.0 μm. It is indicated that the better black display is realized forthe lower transmittance. The results of the simulation show the pixelelectrode, the opposed electrode, and the director of the liquidcrystal, the equipotential lines and the transmittance. In the actualsimulation, the pixel electrode is disposed at the portion of a scale of1 μm to 16 μm of the abscissa, and the pixel electrode is disposed atthe portion of a scale of 19 μm to 35 μm of the abscissa. Moreover, thepixel electrodes adjoin each other at a gap of 2 μm. Because thedisclination and the optical leakage at the portions of the ends of thepixel electrode are noted, however, the portion of the scale of 10 μm to26 μm of the abscissa is shown in an enlarged scale in FIG. 13 and FIG.14. If the pixel electrode is on the flat face, as shown in FIG. 13A,the equipotential lines curve at the end portions of the pixelelectrode. When the first end portion of the first pixel electrode andthe third end portion of the second pixel electrode are disposed at aheight as high as the opposed electrode, as compared with the main faceof the pixel electrode, as shown in FIG. 13B, however, the equipotentiallines are formed along the surface of the pixel electrodes in thevicinity of the first end portion of the first pixel electrode and thethird end portion of the second pixel electrode. Therefore, thecurvatures of the equipotential lines in the vicinity of the first endportion of the first pixel electrode and the third end portion of thesecond pixel electrode are slightly suppressed to reductions in thedisclination in the optical leakage. If the widths of the first endportion and the third end portion are enlarged, as shown in FIG. 14,however, even the equipotential lines having been intrinsically parallelto the flat face having the first pixel electrode and the third pixelelectrode are curved toward the opposed electrode due to the first endportion and the third end portion, as raised with respect to the mainface of the pixel electrode, so that the disclination and the opticalleakage increase. In short, it has been understood that when theadjoining pixel electrode have the potentials of the differentpolarities, the first end portion of the first pixel electrode and thethird end portion of the second pixel electrode are preferably raisedfrom the main face of the pixel electrode and disposed at a high as theopposed electrode, but that the width of the first end portion and thewidth of the third end portion have the optimum values for reducing theoptical leakage and the disclination.

The results of FIG. 13 and FIG. 14 will be summarized with specificnumeral values. The sum of the widths of the optical leakage and thedisclination is designated by x (μm).

When the pixel electrodes are on the flat face, as shown in FIG. 13A,x=9.2 μm;

When the first end portion of the first pixel electrode has a width of1.4 μm and when the third end portion of the second pixel electrode hasa width of 1.4 μm, as shown in FIG. 13B, x=6.8 μm; and

When the first end portion of the first pixel electrode has a width of4.0 μm and when the third end portion of the second pixel electrode hasa width of 4.0 μm, as shown in FIG. 14, x=9.3 μm.

By comparing these three simulation results, the effect to suppress theoptical leakage and the disclination is high when the first end portionand the third end portion have the width of 1.4 μm.

The results of simulations as made by changing the relations between thewidth (L₁) of the first end portion and the sum (x) of the widths of theoptical leakage and the disclination for the cell gap (d), the height(h) of the first end portion, the distance (s) between the first pixelelectrode and the second pixel electrode and the pitch (p) of thepixels, are shown in FIG. 11. In FIG. 11, the abscissa indicates theoverlap width (i.e., the width of the first end portion) of the pixelelectrode and the ridge, and the ordinate indicates the sum of thewidths of the optical leakage and the disclination. It is indicated thatthe quality of the black display is the better for the less sum of thewidths of the optical leakage and the disclination. The simulations aremade with the height of the first end portion 1001 and the height of thethird end portion 1002 being equal. It is indicated that if the heightof the first end portion is 0.5 μm, the height of the third end portionis necessarily 0.5 μm. In the simulations, moreover, the width (L₁) ofthe first end portion and the width (L₂) of the second pixel electrodeare equalized. It is, therefore, indicated that if the width of thefirst end portion is 0.5 μm, the width of the third end portion isnecessarily 0.5 μm.

If the heights of the first end portion and the third end portion aresmall, the effect to suppress the disclination and the optical leakagetends to be low, and it is, therefore, preferable that the heights ofthe first end portion and the third end portion are 0.5 μm or more. Whenthe heights of the first end portion and the third end portion are 0.5μm or more, the cell gap is 4.5 μm or less. It is also understood thatthe sum of the widths of the optical leakage and the disclinationbecomes more than that without the first end portion and the third endportion for the distance of 4.0 μm or less between the pixel electrodes,unless the width of the first end portion and the width of the third endportion are suppressed within 3.0 μm from the ends of the pixelelectrode.

By comparing FIG. 11A and FIG. 11B, it is understood that the effectobtained by raising the first end portion and the third end portion withrespect to the main face of the pixel electrode to the height nearlythat of the opposed electrode appears the more prominent especially asthe cell gap becomes the larger. If the cell gap is large, the electricfield to be established between the opposed electrode and the pixelelectrode is weak so that the equipotential lines are liable to curve atthe end portions of the pixel electrode. Thus, it is understood thatwhen the curvatures of the equipotential lines are large at the endportions of the pixel electrode, the curvatures of the equipotentiallines are effectively suppressed by raising the first end portion andthe third end portion with respect to the main face of the pixelelectrode.

Moreover, the simulations are further made by changing the pixel pitch(p). For the pixel of a pitch of 18 μm and the pixel of a pitch of 43μm, however, the degrees of the optical leakage and the disclination arenot largely changed. This is because the disclination and the opticalleakage are the phenomenon to occur at the end portions of the pixelelectrode (FIG. 11A).

(2) Adjoining Pixel Electrodes at Identical Polarities

In the liquid crystal display device of the gate line inversion drive ina top plan view of a pixel portion in FIG. 2, of the end portions of thepixel electrode, the fourth end portion 204 of the first pixel electrode208 adjoins the second end portion 202 of a third pixel electrode 210,as having the potential of the identical polarity. Therefore, here willbe detailed how to make the structures of the second end portion and thefourth end portion having the potentials of the identical polarity andadjoining each other.

This description will be described with reference to FIG. 2. In theliquid crystal display device for the gate line inversion drive, whenthe pixel electrodes adjoining across the signal line 212B are at thepotentials of the identical polarity, the changes in the orientation ofthe liquid crystal are compared between the cases, in which for thesecond end portion 202 of the third pixel electrode 210 and the fourthend portion 204 of the first pixel electrode 208, the second end portionand the fourth end portion are raised with respect to the main face ofthe pixel electrode so that they are formed to the same level nearlythat of the opposed electrode and to the flat face.

In the simulation model of FIG. 3, it is assumed that the pixelelectrode adjoining the first end portion 303 a is the third pixelelectrode 303 b. It is also assumed that the width (L₁) of the secondend portion and the width (L₂) of the fourth end portion are equalized.

The simulation conditions are identical to those of (1) “the ridges ofthe pixel electrode end portions” excepting that both the first pixelelectrode 303 a and the third pixel electrode 303 b have the potentialof +5 V. Specifically, the potential of the opposed electrode is 0 V,and the distance (s) between the first pixel electrode 303 a and thethird pixel electrode 303 b is 2.0 μm. The height (h) of the second endportion and the height (h) of the fourth end portion are 0.5 μm. Thecell gap (d) is 4.5 μm. The physical properties of the liquid crystal ofthe simulation use the data of ZLI4792 at the room temperature. Thepre-tilt angle and the twist angle of the liquid crystal are 6 degreesand 90 degrees, and the rubbing directions are indicated by 305 and 306.

The results of the simulation are shown in FIGS. 15 and 16. FIGS. 15 and16 show the changes in the transmittance against the overlap width ofthe pixel electrode and the ridge when the pixel electrodes having thepotentials of the identical polarity adjoin each other. It is indicatedthat the more excellent black display is made for the lowertransmittance. FIG. 15A shows the case in which the pixel electrodes areformed on the flat face; FIG. 15B shows the case in which the ends(i.e., the first end portion and the third end portion) of the pixelelectrode are formed over the ridge by 1.4 μm; and FIG. 16 shows thecase in which the ends (i.e., the first end portion and the third endportion) of the pixel electrode are formed over the ridge by 4.0 μm. Inthe actual simulation, the pixel electrode is disposed at the portion ofa scale of 1 μm to 16 μm of the abscissa, and the pixel electrode isdisposed at the portion of a scale of 19 μm to 35 μm of the abscissa.Moreover, the pixel electrodes adjoin each other at a gap of 2 μm.Because the disclination and the optical leakage at the portions of theends of the pixel electrode are noted, however, the portion of the scaleof 10 μm to 26 μm of the abscissa is shown in an enlarged scale in FIG.15 and FIG. 16. The results of FIG. 15 and FIG. 16 will be summarizedwith specific numeral values. The magnitude of the optical leakage isindicated by the maximum (%) of the transmittance. Here is not thedisclination which might otherwise be caused by reversing the pre-tiltdirection at the interface of the alignment film.

When the pixel electrodes are on the flat face, as shown in FIG. 15A,the transmittance of the optical leakage has a maximum of 0.3%;

When the second end portion of the first pixel electrode has a width of1.4 μm and when the fourth end portion of the third pixel electrode hasa width of 1.4 μm, as shown in FIG. 15B the transmittance of the opticalleakage has a maximum of 1.0%; and

When the second end portion of the first pixel electrode has a width of4.0 μm and when the fourth end portion of the third pixel electrode hasa width of 4.0 μm, as shown in FIG. 16 the transmittance of the opticalleakage has a maximum of 1.0%.

When the adjoining pixel electrodes are at the potentials of theidentical polarity, the equipotential lines are formed generally inparallel with the flat face in which the pixel electrodes are formed. Itis in the region between the pixel electrodes where the equipotentiallines curve. Without the ridge below the second end portion and thefourth end portion of the pixel electrode, therefore, the opticalleakage is little, if any (FIG. 15A). Moreover, when the second endportion and the fourth end portion of the pixel electrode are raisedwith respect to the main face of the pixel electrode to the heightnearly that of the opposed electrode, the equipotential lines, asintrinsically parallel to the flat face having the pixel electrode, arecurved by the ridge so that the optical leakage occurs at the portionscorresponding to the two ends of the ridge (FIG. 15B). As the second endportion and the fourth end portion become the wider so that the two endsof the ridge become the closer to the inside of the pixel electrode, theoptical leakages at the two ends of the ridge occur on the inner side ofthe pixel electrode so that the shielding film for shielding the opticalleakage is required to have the larger width (FIG. 16). When the pixelelectrodes adjoining each other are at the potentials of the identicalpolarity, therefore, it has been understood that the better liquidcrystal orientation can be obtained if the second end portion and thefourth end portion of the pixel electrode are at the same height as thatof the main face of the pixel electrode. In other words, a slightoptical leakage occurs at the second end portion and the fourth endportion of the pixel electrode, too, when the adjoining pixel electrodesare at the identical polarity. However, it is predicted that thecountermeasure of raising the end portions of the pixel electroderesults in adverse effects.

The simulation of FIGS. 17 and 18 corresponds to the case in which thepixel electrodes having the equal potentials adjoin each other, andexamines the changes in the transmittance by changing the distancebetween the pixel electrodes. The tendencies are examined by changingthe distance between the pixel electrodes to 2.0 μm, 4.0 μm and 6.0 μm.

From the simulation of FIG. 17 and FIG. 18, it is understood that thecurvatures of the equipotential lines are the less for the shorterdistance between the first pixel electrode and the third pixel electrodewhen the pixel electrodes adjoin each other at the equal potential. FIG.17 and FIG. 18 show the orientation of the liquid crystal when the firstpixel electrode and the third pixel electrode adjoining are at +5 V ofthe identical polarity and when the opposed electrode is at 0 V. Theliquid crystal used is ZLI4792. The pixel electrodes are formed on theflat face. FIG. 17A shows the orientation of the liquid crystal at thetime when the distance between the pixel electrodes is 2.0 μm. FIG. 17Bshows the orientation of the liquid crystal at the time when thedistance between the pixel electrodes is 4.0 μm. FIG. 18 shows theorientation of the liquid crystal at the time when the distance betweenthe pixel electrodes is 6.0 μm.

If the distance between the adjoining pixel electrodes of the identicalpolarity is 2.0 μm or less, as shown in FIG. 17 and FIG. 18, it isunderstood that the curvatures of the equipotential lines are not solarge. When the distance between the pixel electrodes is 2.0 μm or less,therefore, it is predicted that the formation of the second end portionand the fourth end portion of the pixel electrode rising with respect tothe main face of the pixel electrode is adversely effective for theorientation of the liquid crystal. If the second end portion of thepixel electrode and the fourth end portion of the pixel electrode are atthe same height as that of the main face of the pixel electrode, theequipotential lines can be made more parallel to the face having thepixel electrodes to improve the orientation of the liquid crystalbetter.

[Construction 1 of Pixel Portion of Invention]

On the basis of the analyses thus far made, the features of the presentinvention will be described with reference to FIGS. 1 and 2 and FIG. 4.FIG. 1A shows a top plan view of the pixel electrode, and FIG. 1B showsa perspective view of the pixel electrodes arranged in a matrix shape.The top plan view of FIG. 2 shows the positional relations between thesignal lines and the scanning lines and the first to fourth end portionsof the pixel electrodes when the pixel electrodes shown in FIG. 1A arearranged in the 2×2 matrix. The sections, as taken along the chain linesA-A′ and B-B′ from FIG. 2, are presented in FIGS. 4A and 4B. The chainlines A-A′ and B-B′, as presented in the perspective view of the pixelelectrode of FIG. 1B, correspond to the top plan view of FIG. 2 and thesectional view of FIG. 4.

The characteristics of the pixel portion of the present invention willbe described with reference to FIG. 2. The pixel electrode includes thefirst end portion 201, the second end portion 202, the third end portion203 and the fourth end portion 204, and its main face surrounding bythose end portions, and the main face is formed over the flat face.Moreover, the pixel electrode further includes the opposed electrodeopposed to the pixel electrode. The first end portion is extended alongthe first scanning line 207A; the third end portion is extended alongthe second scanning line 207B adjoining the first scanning line 207A;the second end portion is extended along the first signal line 212A; andthe fourth end portion is extended along the second signal line 212Badjoining the first signal line 212A. The two end portions 206A and 206Bof the first end portion 201 are extended along the first signal line212A and the second signal line 212B. The two end portions 205A and 205Bof the third end portion 203 are extended along the first signal line212A and the second signal line 212B. Moreover, the first end portionand the third end portion are formed to have a height nearly that of theopposed electrode with respect to the flat face, and the second endportion and the fourth end portion are formed to have a height nearlythat of the flat face. The present invention can be applied to theliquid crystal display device for the gate line inversion drive.

Moreover, the liquid crystal display device for the gate line inversiondrive is characterized in that the pixel electrode includes the firstpixel electrode 208 and the second pixel electrode 209 adjoining thefirst pixel electrode in the column direction, and in that the first endportion 201 of the first pixel electrode 208 and the third end portion203 of the second pixel electrode adjoin each other. This will bedescribed with reference to the perspective view of FIG. 1B. Over ascanning line 213, there are the first end portion in the first pixelelectrode 208 and the third end portion in the second pixel electrode209. The second end portion and the fourth end portion in the firstpixel electrode to the fourth pixel electrode are at the same height asthat of the main face of the pixel electrodes.

Specifically, for the gate line inversion drive, the first pixelelectrode 208 and the second pixel electrode 209, as opposed to eachother across the first scanning line 207A, as shown in FIG. 2, have thepotentials of polarities different from each other. By forming the firstend portion 201 in the first pixel electrode 208 and the third endportion in the second pixel electrode at a height nearly that of theopposed electrode, the curvatures of the equipotential lines aresuppressed at the first end portion 201 in the first pixel electrode 208and at the third end portion 203 in the second pixel electrode 209thereby to reduce the disclination and the optical leakage effectively(as referred to (1) “the ridges of the pixel electrode end portions”).The second end portion 202 in the first pixel electrode 208 and thefourth end portion 204 in the first pixel electrode are formed on theflat face. The fourth end portion 204 in the first pixel electrode 208and the second end portion 202 in the third pixel electrode 210 have thepotentials of the identical polarity and adjoin each other. It is, themore effective for suppressing the unnecessary curvatures of theequipotential lines and accordingly the disclination and the opticalleakage, that the second end portion of the first pixel electrode andthe fourth end portion of the third pixel electrode, that is, the endportions of the adjoining pixel electrodes at the identical polarity aredisposed on the flat face. This effect is remarkable especially when thedistance between the first pixel electrode and the third pixel electrodeis 2.0 μm or less (as referred to (2) “the ridges of the pixel electrodeend portions”).

In the present invention, moreover, the height of the first end portionand the third end portion are desired to be 0.5 μm or more with respectto the main face of the pixel electrode. In other words, the height ofthe first end portion and the third end portion is desired to be 0.5 μmor closer to the opposed electrode with respect to the main face of thepixel electrode. At this time, the width (L₁) of the first end portionand the width (L₂) of the third end portion, as shown in FIG. 1A, havethe optimum value, so that the effect to reduce the disclination and theoptical leakage cannot be obtained if the optimum value is exceeded.Unless the widths of the first end portion and the second end portionare suppressed within 3.0 μm from the end of the pixel electrode for thecell gap of 4.5 μm or less and for the distance of 4.0 μm between thefirst pixel electrode and the second pixel electrode, the sum of thewidths for the optical leakage and the disclination becomes larger thanthat of the case in which the first end portion and the third endportion are formed to have the same height as that of the main face ofthe pixel electrode. This fact has been described by using the graphs ofFIG. 11 showing the relations between the overlap width (i.e., the widthof the first end portion) of the pixel electrode and the ridge and thesum of the widths for the optical leakage and the disclination (asreferred to (2) “the ridges of the pixel electrode end portions”).

In the sectional view of FIG. 4A showing the end portions of theadjoining pixel electrodes having the potentials of the differentpolarities, there are located the width (L₁) of the first end portion,the width (L₂) of the third end portion, the height of the first endportion and the height (h) of the third end portion. The first endportion 201 and the third end portion 203 rise with respect to the mainface of the pixel electrode and are located at a height close to theopposed electrode. In the sectional view of FIG. 4B showing the endportions of the adjoining pixel electrodes having the potentials of theidentical potential, it is shown that the second end portion 202 and thefourth end portion 204 are formed on the flat face.

In the liquid crystal display device for the source line inversiondrive, the positional relations of the end portions of the pixelelectrode may be thought by replacing the first signal line 212A of FIG.2 and FIG. 1B by the first scanning line and the second signal line 212Bby the second scanning line. Naturally, the first scanning line 207A isreplaced by the first signal line, and the second scanning line 207B isreplaced by the second signal line.

Specifically, according to the present invention, the liquid crystaldisplay device for the source line inversion drive is characterized: thepixel electrode includes the band-shaped first, second, third and fourthend portions and the main face surrounded by these end portions; in thatthe main face is formed on the flat face; in that there is furtherincluded the opposed electrode opposed to the pixel electrode; in thatthe first end portion is extended along the first signal line, the thirdend portion is extended along the second signal line adjoining the firstsignal line, the second end portion is extended along the first scanningline, and the fourth end portion is extended along the second scanningline adjoining the first scanning line; in that the first end portionand the third end portion are extended at their two end portions alongthe first scanning line and the second scanning line; in that the firstend portion and the third end portion are nearly as high as the opposedelectrode with respect to the flat face; and in that the second endportion and the fourth end portion are at the same height as that of theflat face.

Moreover, the liquid crystal display device is characterized: in thatthe pixel electrode includes the first pixel electrode and the secondpixel electrode adjoining the former in the row direction; and in thatthe first end portion of the first pixel electrode and the third endportion of the second pixel electrode adjoin each other.

Moreover, the liquid crystal display device is characterized: in thatthe first end portion and the third end portion are disposed at a heightof 0.5 μm or closer to the opposed electrode; and in that the width ofthe first end portion and the width of the third end portion are 3.0 μmor less from the end of the pixel electrode when the liquid crystaldisplay device has a cell gap of 4.5 μm or less and when the distancebetween the first pixel electrode and the second pixel electrode is 4.0μm or less.

In the ordinary liquid crystal display device of the active matrix type,the pixel electrode is mostly formed over the scanning lines and thesignal lines. Therefore, the end portions of the pixel electrode arenecessarily formed mostly to rise with respect to the main face of thepixel electrode to a height close to the opposed electrode. However, theeffect to reduce the disclination and the optical leakage is notobtained merely by raising the end portions of the pixel electrode withrespect to the main face of the pixel electrode. It is assumed, forexample, that the portions of the end portions of the pixel electrodeover a scanning line 3005 and the (not-shown) signal line rise withrespect to the main face of the pixel electrode, as shown in aperspective view of the pixel electrodes arranged in a matrix shape inFIG. 31A. With this simple construction, the disclination and theoptical leakage, as caused generally in parallel with the scanning line3005 when in the gate line inversion drive, for example; are suppressedbecause the end portions of the pixel electrodes rise with respect tothe main face of the pixel electrodes. However, the end portion 3010 ofa pixel electrode 3006 and the end portion of a pixel electrode 3008, asadjoining each other in the identical polarity, rise with respect to themain face of the pixel electrodes so that the disclination and theoptical leakage will occur in parallel with the signal line of the pixelelectrodes.

When the pixel TFTs to be connected with the pixel electrodes are to beconstructed, the end portions of the pixel electrodes may be locallyraised by the thicknesses of the storage capacities and thesemiconductor layers connected in series with the pixel TFTs, as shownin the perspective view of the pixel electrodes arranged in the matrixshape in FIG. 31B. However, the mere rises of the end portions of thepixel electrodes, as locally caused merely by the thicknesses of thestorage capacities with respect to the main face of the pixelelectrodes, could not attain the effect to reduce the disclination andthe optical leakage. In the liquid crystal display device for the sourceline inversion drive, for example, it is nonsense to raise the endportions of the pixel electrodes along the scanning line 3005 withrespect to the main face of the pixel electrodes. Specifically, independence upon the gate line inversion drive or the source lineinversion drive of the liquid crystal display device, it is necessary toselect whether the portions rising from the main face of the pixelelectrode, such as the first end portion and the third end portion, areto be formed along the scanning line or the signal line. As shown in thetop plan view of the pixel electrodes of FIG. 1A, especially, the twoend portions 206A and 206B of the first end portion 201 and the two endportions 205A and 205B of the third end portion of the pixel electrode,as contacting with the pixel electrode of the different polarity andhaving the easily curving equipotential lines, have to be raised withrespect to the main face of the pixel electrode to a height close to theopposed electrode. The construction of the perspective view of FIG. 31Bcannot suppress the optical leakage and the disclination, as mightotherwise occur at the end portion 3012 of the pixel electrode.

In short, the construction of the pixel portion of the present inventionhas the structure, which has been decided by considering the potentialsof the adjoining pixel electrodes and the equipotential lines caused bythe structure of the pixel electrodes, but is not absolutely differentfrom the structure which is necessarily made. Moreover, the structure isobtained by examining how to establish the equipotential linessystematically by the simulation so that it should be highly appreciatedin its effects, as compared with the method of the prior art forreducing the disclination and the optical leakage.

In the simulation, as shown in FIG. 3, the section of the ridge 304below the first end portion and the third end portion of the pixelelectrode is formed into a rectangular shape. However, the presentinvention can also be applied to the simulation model of FIG. 3, inwhich the angle (as will be called the “taper angle of the ridge”), asmade between the side face of the ridge and the face contacting with themain face of the pixel electrode is 90 degrees or less. Where the taperangle of the ridge 304 is less than 90 degrees in the sectional view ofFIG. 5A showing the end portion of the pixel electrode, the abruptchange in the electric field in the vicinity of the crests of the ridgecan be suppressed, as compared with the structure in which the ridge hasthe rectangular section. Then, the electric field abruptly changes atthe crests of the rectangular ridge, as resulted by the simulation ofFIG. 15B, so that the phenomenon of the locally high transmittance canbe preferably prevented. Similar discussions apply to the case in whichthe section of the ridge is curved, as shown in the top plan view of theend portions of the pixel electrode in FIG. 5B. Thus, even when thesection of the ridge below the first end portion and the third endportion of the pixel electrode is not rectangular, on the contrary, itis predicted that the optical leakage and the disclination are notincreased by the first end portion and the third end portion, if thewidth (L₁) of the first end portion and the width (L₂) of the third endportion of the pixel electrode are suppressed within 3.0 μm, when thefirst end portion and the third end portion have a height (h) of 0.5 μmor more, when the cell gap is 4.5 μm or less and when the distance (s)between the pixel electrodes is 4.0 μm or less. Here, the width (L₁) ofthe first end portion and the width (L₂) of the third end portion areapplied to the portions of the pixel electrode, which rise locally withrespect to the main face of the pixel electrode.

[Construction 2 of Pixel Portion of the Invention]

Here will be described the construction of the pixel portion of thepresent invention. A comparison is made between the simulation resultshaving examined how the optical leakage and the disclination occurreddepending upon whether the adjoining pixel electrodes of FIG. 13 to FIG.16 have the potentials of the identical or different polarities. It isthought better that the height of the end portions of the pixelelectrode is locally increased where the equipotential lines make largecurvatures, so as to suppress the curvatures of the equipotential linesof the pixel electrode end portions.

However, how much the end portions of the pixel electrode are to beraised with respect to the main face of the pixel electrode has to bedetermined on the basis of the curving degree of the equipotential linesformed by the pixel electrodes adjoining each other. This could beunderstood by comparing the simulation results of FIG. 13 to FIG. 16.Specifically, if the heights of the end portions of the pixel electrodeare carelessly increased nearly to that of the opposed electrode evenwith little curvature of the equipotential lines, this determinationwill increase the disclination and the optical leakage (FIG. 15 and FIG.16). When the equipotential lines prominently curve at the end portionsof the pixel electrode, however, the end portions of the pixel electrodeare raised with respect to the main face of the pixel electrode to aheight close to the opposed electrode (FIG. 13 and FIG. 14).

If this concept is developed, moreover, the heights of the end portionsof the pixel electrode may be made the larger for the more intensecurvatures of the equipotential lines at the end portions of the pixelelectrode. In short, it is effective for preventing the optical leakageand the disclination to determine the heights of the end portions of thepixel electrode in accordance with the curving degree of theequipotential lines.

The description will be made with reference to the top plan view of thepixel electrode of FIG. 6A. In the case of a rectangular pixel electrode258, the intense curvatures of the equipotential lines are specified tooccur at the vicinities 255A and 255B, and 256A and 256B to the crestsof the pixel electrode. At these vicinities 255A and 255B, and 256A and256B of the crests of the pixel electrodes close to the two pixelelectrodes having the potentials of the different polarities, theseequipotential lines are intensely curved by the influences of the pixelelectrodes having the potentials of the different polarities. In therectangular pixel electrodes, the vicinities of the crests of the pixelelectrode, e.g., the two end portions 256A and 256B of a first endportion 251 may be raised with respect to the central portion 263 of thefirst end portion 251 of the pixel electrode. Moreover, the two endportions 255A and 255B of a third end portion 253 of the pixel electrodeare locally raised with respect to the central portion of the third endportion 253. Here, the central portion of the first end portion islocated at a position bisecting a segment which is formed of two points:one point (A) on the end of the pixel electrode, as contained in the twoend portions 256A of the first end portion; and an intersection point(B) between the straight line extending from that point (A) in parallelwith the row direction of the pixels and the other of the two endportions 256B of the first end portion. The central portion of the thirdend portion can be defined if the description thus far made is changedfrom the first end portion to the third end portion.

The characteristics of the pixel electrode of the present invention willbe described with reference to the top plan view of the pixel portion ofFIG. 7, in which the pixel electrodes are arranged in the matrix shape.The first to fourth pixel electrodes 258 to 261 are shown in a matrix of2×2. For the gate line inversion drive, the pixel electrodes having thepotentials of polarities different from that of the first pixelelectrode 258 are the second pixel electrode 259 and the fourth pixelelectrode 261. Specifically, one 256A of the two end portions 256A and256B of the first end portion 251 of the first pixel electrode adjoinsthe second pixel electrode 259 and the fourth pixel electrode 261 havingthe potentials of the polarity different from that of the first pixelelectrode. Then, the equipotential lines are intensely curved at the twoend portions 256A of the first end portion of the first pixel electrodeby the influences of the electric field which is established by thesecond pixel electrode and the fourth pixel electrode and by the two endportions 256A of the first end portion of the first pixel electrode.

Of the first to fourth pixel electrodes shown in the top plan view ofFIG. 7, therefore, the portions close to the two pixel electrodes havingthe polarities of the different polarities, such as the two end portions256A and 256B of the first end portion and the two end portions 255A and255B of the third end portion are desired to be locally raised.Specifically, if the heights of the end portions of the pixel electrodeare determined according to the curving degree of the equipotentiallines at the pixel electrode end portions, the two end portions of thefirst end portion and the two end portions of the third end portion havelarge curvatures of the equipotential lines so that they necessarilyhave to be raised with respect to the main face of the pixel electrode.In other words, it is necessary to set the two end portions of the firstend portion and the two end portions of the third end portion atpositions close to the opposed electrode.

For example, the liquid crystal display device for the gate lineinversion drive may be given a structure in which the two end portionsof the first end portion and the third end portion, as located close tothe scanning line 263, of the end portions of the pixel electrode arelocally raised, as shown in the perspective view of FIG. 6B showing thepixel electrodes arranged in the matrix shape.

With reference to FIG. 7, the liquid crystal display device for the gateline inversion drive according to the present invention is constructedsuch that the pixel electrode includes the band shaped first end portion251, second end portion 252, third end portion 253 and fourth endportion 254, and the main face enclosed by those end portions. This mainface is formed over the flat face and has the opposed electrode opposedto the pixel electrode. Moreover, the first end portion is extendedalong the first scanning line 257A; the third end portion is extendedalong a second scanning line 257B adjoining the first scanning line; thesecond end portion is extended along a first signal line 262A; and thefourth end portion is extended along a second signal line 262B adjoiningthe first signal line. The two end portions 255A and 255B, and 256A and256B of the first end portion and the third end portion are extendedalong the first signal line and the second signal line. The first endportion and the third end portion are disposed at a height close to theopposed electrode with respect to the flat face, and the second endportion and the fourth end portion are disposed at the height equal tothat of the flat face.

In this liquid crystal display device, moreover, the present inventionis characterized in that the two end portions of the first end portionare disposed at a height closer to the opposed electrode than thecentral portion of the first end portion, and in that the two endportions of the third end portion are disposed at a height closer to theopposed electrode than the central portion of the third end portion.

Specifically, the present invention is characterized in that the two endportions of the first end portion are disposed at a height closer by asignificant different of 0.2 μm or closer to the opposed electrode thanthe central portion of the first end portion, and in that the two endportions of the third end portion are disposed at a height closer by 0.2μm or closer to the opposed electrode than the central portion of thethird end portion.

Alternatively, the present invention is characterized in that the twoend portions of the first end portion are disposed at a height closer bya significant different of 0.5 μm or closer to the opposed electrodethan the central portion of the first end portion, and in that the twoend portions of the third end portion are disposed at a height closer by0.5 μm or closer to the opposed electrode than the central portion ofthe third end portion.

If the pixel electrode rises into a ridge shape by 0.2 μm or more, or0.5 μm or more, there is a significant effect to change how theequipotential lines are established to change the orientation of theliquid crystal, as seen from the graphs showing the results of thesimulation as shown in FIG. 11.

FIGS. 8A and 8B present the sectional views of the pixel electrode, astaken along chain lines C-C′ and D-D′ from the top plan view of FIG. 7.In FIG. 8B, there are defined the height (hi) of the first end portionand the third end portion of the pixel electrode 261, and the width (L₁)of the first end portion. Here, the fact that the first end portion hasthe height h1, namely, that the distance between the face contactingwith the main face of the pixel electrode and the uppermost end portionof the first end portion is h1 will mean that the first end portion ofthe pixel electrode is at a height close by h1 to the opposed electrode.As shown in FIG. 8A, the two end portions of the first end portion ofthe pixel electrode 259 are raised to a height h2 with respect to thecentral portion of the first end portion. Here, the fact that thedistance between the face contacting with the central portion of thefirst end portion and the uppermost end portion of the two end portionsof the first end portion is h2 will mean that the two end portions ofthe first end portion are disposed at a height closer by h2 to theopposed electrode than the central portion.

In the liquid crystal display device for the source line inversiondrive, it is sufficient to replace the scanning lines by the signallines and the signal lines by the scanning lines.

[Example of Application Range of the Invention]

The structure of the pixel portion thus made according to the presentinvention is that the lines of electric power when the electric field isapplied are normal to the formed flat face of the pixel electrode, sothat it can be widely used as means for reducing the orientation failureof the liquid crystal for both the orientation systems of the normallywhite mode and the normally black mode.

If the orientation of the liquid crystal is not induced by thecorrugations, moreover, the present invention can be applied to theorientation system using the semantic liquid crystal. For example, thepresent invention can be applied to the liquid crystal display deviceusing a ferro-electric liquid crystal or an anti-ferro-electric liquidcrystal. Moreover, the present invention can also be applied to theliquid crystal display device using the material which has been set byadding a liquid polymer to the semantic liquid crystal and byirradiating it with a beam (e.g., an ultraviolet ray).

The construction of the pixel portion of the present invention can bewidely used as the means for adjusting the electric field distributionin the display device in which the optical modulation layer is opticallymodulated by applying a voltage thereto by a semiconductor element.

Especially in the projection type liquid crystal display device, theoptical leakage and the disclination are enlarged by the optical systemusing lenses and are projected on the screen. Therefore, the presentinvention is effective especially in the projection type liquid crystaldisplay device.

The first end portion, the second end portion, the third end portion andthe fourth end portion of the present invention need not be rectangular,as shown in the top plan views. These end portions may be freelydesigned on the basis of the concept in which the portions of theequipotential lines to curve intensely at the time of driving the liquidcrystal display device are raised at the end portions of the pixelelectrode than the main face of the pixel electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are a top plan view and a perspective view showing apixel portion of the present invention;

FIG. 2 is a top plan view showing the pixel portion of the presentinvention;

FIG. 3 is a sectional view showing a model of a simulation;

FIGS. 4A and 4B are sectional views showing the pixel portion of thepresent invention;

FIGS. 5A and 5B are sectional views showing the pixel portion of thepresent invention;

FIGS. 6A and 6B are a top plan view and a perspective view showing apixel portion of the present invention;

FIG. 7 is a top plan view showing the pixel portion of the presentinvention;

FIGS. 8A and 8B are sectional views showing the pixel portion of thepresent invention;

FIG. 9 is a top plan view showing one example of the pixel portion ofthe present invention;

FIG. 10 is a top plan view showing one example of the pixel portion ofthe present invention;

FIGS. 11A and 11B are diagrams plotting relations between the width of afirst end portion and the sum of an optical leakage and the width of adisclination;

FIG. 12 is a schematic diagram showing a principle in which the opticalleakage and the disclination occur;

FIGS. 13A and 13B are sectional views showing the simulation results inwhich the adjoining pixel electrodes are at potentials of differentpolarities;

FIG. 14 is a sectional view showing the simulation results in which theadjoining pixel electrodes are at potentials of different polarities;

FIGS. 15A and 15B are sectional views showing the simulation results inwhich the adjoining pixel electrodes are at potentials of an identicalpolarity;

FIG. 16 is a sectional view showing the simulation results in which theadjoining pixel electrodes are at potentials of an identical polarity;

FIGS. 17A and 17B are sectional views showing the simulation results inwhich the adjoining pixel electrodes are at potentials of an identicalpolarity;

FIG. 18 is a sectional view showing the simulation results in which theadjoining pixel electrodes are at potentials of an identical polarity;

FIGS. 19A and 19B are top plan views showing a process for manufacturingan active matrix substrate;

FIGS. 20A and 120B are top plan views showing a process formanufacturing the active matrix substrate;

FIG. 21 is a top plan view showing a process for manufacturing theactive matrix substrate;

FIG. 22 is a top plan view showing one example of the pixel portion ofthe present invention;

FIG. 23 is a sectional view showing one example of the active matrixsubstrate of the present invention;

FIG. 24 is a sectional view showing a liquid crystal display device;

FIGS. 25A to 25F are perspective views showing examples of electronicdevices;

FIGS. 26A to 26D are perspective views showing examples of theelectronic devices;

FIGS. 27A to 27C are perspective views showing examples of theelectronic devices;

FIGS. 28A and 28B are schematic diagrams showing equipotential lines inwhich the adjoining pixel electrodes are at potentials of an identicalpolarity:

FIGS. 29A to 29C are schematic diagrams showing equipotential lines inwhich the adjoining pixel electrodes are at potentials of differentpolarities:

FIGS. 30A and 30B are diagrams showing the polarities of the voltage tobe applied to the pixels at the time for a source line inversion drive;and

FIGS. 31A and 31B are perspective views showing examples to be comparedwith the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In order to retain the aperture ratio of the pixel portion of the liquidcrystal display device, it is a recommended method to form the endportions of the pixel electrodes over the scanning lines, the signallines and the capacity electrodes by forming interlayer films over thescanning lines, the signal lines and the capacity electrodes. In the topplan views showing the embodiments of the present invention, however,the scanning lines, the signal lines and the pixel electrodes areconsciously shown distantly so that the positional relations between thecharacteristic portions of the pixel electrodes and the scanning linesand the signal lines may be easily understood. The method ofmanufacturing the recommendable liquid crystal display device will bedescribed in detail in connection with the embodiments.

In the liquid crystal display device for the source line inversiondrive, as shown in a top plan view of FIG. 9, a first end portion 201 ofa first pixel electrode 208 and a third end portion 203 of a secondpixel electrode 209, as opposed to each other across a signal line 206,are raised with respect to the main face of the pixel electrodes.

When the adjoining pixel electrodes are at the potentials of thedifferent polarities, the equipotential lines easily curve at the endportions of the adjoining pixel electrodes. Specifically, theequipotential lines easily curve between the first pixel electrode 208and the second pixel electrode 209. Therefore, it is recommended thatthe first end portion 201 and the third end portion 203 of the pixelelectrodes having the easily curving equipotential lines are raised withrespect to the main face of the pixel electrodes.

In case the first pixel electrode 208 and a third pixel electrode 210are at the potentials of an identical polarity, the equipotential linesmake a curvature in the gap between the first pixel electrode 208 andthe third pixel electrode 210, which is not considerably large in thegap between the pixel electrodes of the identical potential. When thefirst pixel electrode 208 and the third pixel electrode 210 adjoin eachother, therefore, it is recommended that the second end portion and thefourth end portion of the pixel electrode positioned across the gap areformed at the same level as that of the main face of the pixelelectrodes.

In FIG. 10, the pixel electrodes are formed into a polygonal shapehaving crests equal to or more than four. It is assumed that the driveis the gate line inversion drive. In the liquid crystal display devicehaving a small pixel size, it is advantageous for writing the charges inthe storage capacity to perform the gate line inversion drive.

A first end portion 251 and a third end portion 253 of a first pixelelectrode 258 and a second pixel electrode 259, as opposed each otheracross a scanning line 257, are raised with respect to the main face ofthe pixel electrodes. Moreover, the two end portions 256A and 256B ofthe first end portion and the two end portions 255A and 255B of thethird end portion are raised from the central portion of the first endportion and the central portion of the third end portion with respect tothe main faces of the pixel electrodes so that the curvatures of theequipotential lines may be corrected in the serious curvature region ofthe equipotential lines. The second end portion and the fourth endportion of the pixel electrodes are at the same level of that of themain faces of the pixel electrodes.

Below the first end portion and the third end portion, it is recommendedto pattern and form a photosensitive organic resin film and an organicresin film by a photolithography process. It is naturally possible topattern and form an inorganic film such as a silicon oxide film, asilicon nitride film or a silicon oxynitride film, too.

In order to make the two end portions of the first end portion locallyhigher than the central portion of the first end portion, it isrecommended to form the photosensitive resin film separately twice. Itis also recommended to form the semiconductor layer, the scanning lines,and the signal lines and so on of the element substrate at the two endportions of the first end portion thereby to form the raised regionsselectively with respect to the main face of the pixel electrodes.

Embodiment 1

Embodiments of the present invention will now be described withreference to FIGS. 19 to 23.

First, an electrically conducting film is formed on a substrate 601having an insulating surface shown in a sectional view of FIG. 23B, andis patterned to form a scanning line 602. The scanning line also worksas a light-shielding film for protecting a semiconductor layer fromlight that will be formed later. Here, a quartz substrate is used as asubstrate 601, and a laminated-layer structure of a polysilicon film (50nm thick) and a tungsten silicide (W—Si) film (100 nm thick) is used asthe scanning line 602. Further, the polysilicon film prevents thesubstrate from being contaminated with the tungsten silicide.

Next, an insulating film 603 is formed maintaining a thickness of 100 to1000 nm (typically, 300 to 500 nm) to cover the scanning line 602. Here,a silicon oxide film having a thickness of 100 nm formed by the CVDmethod and a silicon oxide film having a thickness of 280 nm formed bythe LPCVD method are laminated one upon the other.

Then, an amorphous semiconductor film is formed maintaining a thicknessof 10 to 100 nm. Here, the amorphous silicon film is formed maintaininga thickness of 69 nm by the LPCVD method. Next, the amorphous siliconfilm is crystallized by a technology disclosed in Japanese PatentLaid-Open No. 8-78329. According to the technology disclosed in thispublication, a metal element is selectively added to the amorphoussilicon film to promote the crystallization followed by the heattreatment to form a crystalline silicon film which spreads starting fromthe region where the metal element is added. Here, nickel is used as ametal element for promoting the crystallization and, then, a heattreatment (450° C., one hour) is executed for dehydrogenation, followedby another heat treatment (600° C., 12 hours) for crystallization.

Then, Ni is put to the bettering from the region where the active layerof TFT is formed. The region of the active layer of TFT is covered witha mask (silicon oxide film), phosphorus (P) is added to a portion of thecrystalline silicon film and is heat-treated (at 600° C. in a nitrogenatmosphere for 12 hours).

Then, after the mask is removed, unnecessary portions of the crystallinesilicon film are removed by patterning to form semiconductor layers 604a and 604 b. The semiconductor layers 604 a and 604 b are the samesemiconductor layers 604. FIG. 19A is a top view of the pixel after thesemiconductor layer is formed. There are shown a scanning line 602 and asemiconductor layer 604.

Next, to form a storage capacity, a resist is formed, and a portion(region for forming the storage capacity) 604 b of the semiconductorlayer is doped with phosphorus.

Then, the resist is removed and an insulating film is formed to coverthe semiconductor layer. Then, to increase the capacity of the storagecapacitor, a resist is formed, and the insulating film is removed fromthe region 604 b where the storage capacity is to be formed.

Then, an insulating film (gate insulating film 605) is formed by thethermal oxidation. Due to this thermal oxidation, the gate-insulatingfilm finally acquires a thickness of 80 nm. On the region where thestorage capacity is to be formed, there is formed an insulating filmhaving a thickness smaller than that of other regions. It is desiredthat the insulating film has a thickness of 40 to 50 nm on the regionwhere the storage capacity is to be formed.

Next, the channel doping is effected onto the whole surface orselectively to add p-type or n-type impurities at a low concentration tothe region that serves as the channel region of the TFT. The step ofthis channel doping is the one for controlling the threshold voltage ofthe TFT. Here, boron is added by the ion-doping method by excitingdiborane (B₂H₆) by plasma but without effecting the mass separation. Itis, of course, allowable to employ the ion plantation method byeffecting the mass separation.

Next, contact holes that reach the scanning lines are formed by etchingthe insulating film.

Then, an electrically conducting film is formed and is patterned to forma gate electrode 606 a and a capacitor wiring 606 b. Here, use is madeof a laminated-layer structure of a silicon film (150 nm thick) dopedwith phosphorus and a tungsten silicide film (150 nm thick). The storagecapacitor is formed by parts of the capacitor wiring and of thesemiconductor layer with the insulating film 605 as a dielectric.

FIG. 19B is a top view of a pixel after the gate electrode and thecapacitor wiring are formed. The gate electrode 606 a is electricallyconductive to the scanning line 602 through a contact hole 801. A regionwhere the semiconductor layer 604 is overlapped on the capacitor wiring606 b via an insulating film works as the storage capacitor.

Then, by using the gate electrode and the capacitor wiring as masks,phosphorus is added at a low concentration in a self-aligned manner. Theconcentration of phosphorus in the region to where it is added at a lowconcentration, is adjusted to be from 1×10¹⁶ to 5×10¹⁸ atoms/cm³ and,typically, from 1×10¹⁶ to 5×10¹⁸ atoms/cm³.

Next, a resist is formed and phosphorus is added at a high concentrationby using the resist as a mask, thereby to form a region containingimpurities at a high concentration that serves as a source region or adrain region. The phosphorus concentration in the region of the highimpurity concentration is adjusted to be from 1×10²⁰ to 1×10²¹ atoms/cm³and, typically, from 2×10²⁰ to 5×10²⁰ atoms/cm³. In the semiconductorlayer, a region overlapped on the gate electrode serves as a channelregion, and a region covered with a resist serves as an impurity regionof a low concentration and works as an LDD region. After the impuritiesare added, the resist is removed.

Though not diagramed, the region that becomes an n-channel TFT iscovered with a resist, and boron is added to form a source region or adrain region in order to form a p-channel TFT used for a driver circuitformed on the same substrate as the pixels.

Next, after the resist is removed, a passivation film 607 is formed tocover the gate electrode 606 a and the capacitor wiring 606 b. Here, asilicon oxide film is formed maintaining a thickness of 70 nm. Next, theheat treatment is effected to activate the n-type or p-type impuritiesadded into the semiconductor layer at their respective concentration.Here, the heat treatment is effected at 950° C. for 30 minutes.

Then, an interlayer insulating film 608 of an inorganic material isformed. In this Embodiment, a silicon oxynitride film is formedmaintaining a thickness of 800 nm.

Then, a contact hole is formed to reach the semiconductor layer, and anelectrode 610 and a signal line 609 are formed. In this Embodiment, theelectrode and the signal lines are formed of a laminated-layer film of afour-layer structure in which a Ti film is formed maintaining athickness of 60 nm, a TiN film is formed maintaining a thickness of 40nm, an aluminum film containing Si is formed maintaining a thickness of300 nm, and a TiN film is formed maintaining a thickness of 100 nm allby sputtering in a continuous manner.

FIG. 20A is a top view of the pixel after the electrode and the signallines are formed. The signal line 609 is electrically conductive to thesemiconductor layer through the contact hole 802. The electrode 803 iselectrically conductive to the semiconductor layer through the contacthole 803.

Then, the hydrogenation treatment is effected at 350° C. for one hour.

Next, an interlayer insulating film 612 of an organic resin material isformed. An acrylic resin film of 1.0 μm thickness is used here.Thereafter, a light-shielding electrically conducting film is formedmaintaining a thickness of 100 nm on the interlayer-insulating film tothereby form a light-shielding film 613.

Here, a top plan view of a pixel portion after a shielding film 613 wasformed is shown in FIG. 20B. The shielding film 613 has a role toprevent the optical leakage and the disclination from being visuallyconfirmed, and a role to shield the electric field, as established as aresult that the signal line has a potential, so that the orientation ofthe liquid crystal may not be disturbed by the potential owned by thesignal line. For this, the shielding layer overlaps a signal line 609.

The shielding film 613 over the signal line 609 is formed in the gapbetween the pixel electrode and the pixel electrode, as will bedescribed hereinafter. As a result, the corrugations due to the filmthickness of the shielding film are not formed at the end portions ofthe pixel electrodes along the signal line. The end portions of a pixelelectrode 616 along the signal line are formed on a flat face.

Next, an insulating film 614 is formed to have a thickness of 100 nm.This insulating film forms a silicon oxynitride film having a thicknessof 100 nm to 300 nm.

Next, a photosensitive resin film is used to perform a photolithographystep thereby to form a ridge 615 of a thickness of 0.5 μm along thescanning line. The photosensitive resin film uses a material whichlowers the viscosity by diluting BPR-107VL of JSR Company with PGMEA(Propylene Glycol Monomethyl Ether Acetate).

Next, contact holes are formed to reach the electrodes. Next, atransparent conductive film (e.g., an indium-tin oxide (ITO) film) of100 nm is formed and is patterned to form the pixel electrodes 616.

Here, there can be formed a storage capacitor 617 by making the pixelelectrodes and the shielding film 613 into the electrodes and theinsulating film 614 into a dielectric member.

Here, the top plan view of the pixels after the pixel electrodes 616were formed is shown in FIG. 21. An electrode 610 and the pixelelectrode are conducted through a contact hole 804. The ridge 615, asformed along the scanning line, has a pattern of a slender square. Thedistance (s) between the pixel electrode and the pixel electrode is 2.0μm, and the overlap width (L) between the pixel electrode and the ridgeis 1.0 μm.

The substrate thus manufactured by the steps thus far described will becalled the “active matrix substrate”.

The top plan view showing the electrodes, the wiring lines and thesemiconductor layer formed in the pixel portion are presented in FIG.22. A section, as cut along chain lines E-E′ and F-F′ from the top planview of FIG. 22, is present in FIG. 23.

The present embodiment is only one example, and it is needless to saythat the present invention should not be limited to the steps of thepresent embodiment. For example, each conductive film may be exemplifiedby one made of tantalum (Ta), titanium (Ti), molybdenum (Mo), tungsten(W), chromium (Cr) or silicon (Si).

The active matrix substrate of the present embodiment can be used in atransmission type liquid crystal display device. When a conductive filmhaving a function to reflect a light is used as a pixel electrode inplace of the transparent conductive film, the active matrix substrate ofthe present embodiment can be used in a reflection liquid crystaldisplay device.

Embodiment 2

This embodiment deals with the steps for fabricating a liquid crystaldisplay device of the active matrix type using the active matrixsubstrate fabricated in Embodiment 1. The description refers to FIG. 24.

First, the active matrix substrate is obtained in accordance withEmbodiment 1.

Next, a transparent electrode 701 of a transparent electricallyconducting film is formed on a light-transmitting substrate 700. In thisembodiment, the thus constituted substrate is called opposing substrate.

Then, an oriented film 703 is formed on the active matrix substrate andon the opposing substrate, and is rubbed. The liquid crystal displaydevice fabricated according to this Embodiment is a panel of theprojection type having a diagonal size of from about 0.3 inches to about1 inch. In the panel of this kind, the pixels have a size of as small as10 μm to 20 μm, and the defect caused by spacers becomes no longernegligible. The liquid crystal display device of this embodiment,therefore, uses no spacer.

The active matrix substrate on which the pixel portions and the drivercircuits are formed, is stuck to the opposing substrate with a sealingmember. The sealing member contains a filler, and the two pieces ofsubstrates are stuck together maintaining a uniform gap due to thefiller. The cell gap between the pixel portions is 4.5 μm.

Thereafter, a liquid crystal material 704 is poured into between the twosubstrates, and is completely sealed with a sealing agent (not shown).The liquid crystal material 704 may be a known material. Thus, theliquid crystal display device of the active matrix type is completed asshown in FIG. 24. As required, further, the active matrix substrate orthe opposing substrate is divided into a desired shape. Further, apolarizer plate is suitably provided relying upon the known technology.An FPC is stuck, too, according to the known technology.

Referring to Embodiment 1, the liquid crystal display device is formedthat is constituted the following; the cell gap to be 4.5 μm, thedistance between the pixel electrodes is 2.0 μm, the height to be 0.5μm, and the widths (L) of overlapping portion with the pixel electrodeand the height to be 1.0 μm. It is estimated that the sum of widths bywhich the leakage of light and the disclination are decreased is 2.2 μmas compared with when there is no height by the graph of FIG. 11.

Thus fabricated liquid crystal display panel can be used as a displayunit for a variety of electronic devices.

Embodiment 3

The liquid crystal display device formed by implementing an embodimentbetween above-mentioned Embodiments 1 and 2 can be applied to variouselectro-optical equipments. Thus the present invention can be applied toall of the electronic equipments having these electro-optical devices asthe display portion.

The following can be given as examples of the electronic equipment:video cameras; digital cameras; projectors; head mounted displays(goggle type display); car navigation systems; car stereo; personalcomputers; portable information terminals (such as mobile computers,portable telephones and electronic notebook). An example of these isshown in FIGS. 25, 26 and 27.

FIG. 25A shows a personal computer, and it includes a main body 2001, animage input section 2002, a display portion 2003, and a keyboard 2004.The present invention is applicable to the display portion 2003.

FIG. 25B shows a video camera, and it includes a main body 2101, adisplay portion 2102, a voice input section 2103, operation switches2104, a battery 2105, and an image receiving section 2106. The presentinvention is applicable to the display portion 2102.

FIG. 25C shows a mobile computer, and it includes a main body 2201, acamera section 2202, an image receiving section 2203, operation switches2204, and a display portion 2205. The present invention is applicable tothe display portion 2205.

FIG. 25D shows a goggle type display, and it includes a main body 2301;a display portion 2302; and an arm section 2303. The present inventionis applicable to the display portion 2302.

FIG. 25E shows a player using a recording medium which records a program(hereinafter referred to as a recording medium), and it includes a mainbody 2401; a display portion 2402; a speaker section 2403; a recordingmedium 2404; and operation switches 2405. This player uses DVD (digitalversatile disc), CD, etc. for the recording medium, and can be used formusic appreciation, film appreciation, games and Internet. The presentinvention is applicable to the display portion 2402.

FIG. 25F shows a digital camera, and it includes a main body 2501; adisplay portion 2502; a view finder 2503; operation switches 2504: andan image receiving section (not shown in the figure). The presentinvention can be applied to the display portion 2502.

FIG. 26A is a front-type projector, and it includes a projection device2601 and a screen 2602. The present invention is applicable to a liquidcrystal display device 2808 which comprises one of the projection device2601.

FIG. 26B is a rear-type projector, and it includes a main body 2701, aprojection device 2702, a mirror 2703, and a screen 2704. The presentinvention is applicable to a liquid crystal display device 2808 whichcomprises one of the projection device 2702.

FIG. 26C is a diagram showing an example of the structure of theprojection devices 2601, 2702 in FIGS. 26A and 26B. The projectiondevice 2601 or 2702 comprises a light source optical system 2801,mirrors 2802, 2804 to 2806, dichroic mirrors 2803, a prism 2807, liquidcrystal display devices 2808, phase difference plates 2809, and aprojection optical system 2810. The projection optical system 2810 iscomposed of an optical system including a projection lens. This exampleshows an example of three-plate type but not particularly limitedthereto. For instance, the invention may be applied also to a singleplate type optical system. Further, in the light path indicated by anarrow in FIG. 26C, an optical system such as an optical lens, a filmhaving a polarization function, a film for adjusting a phase difference,and an IR film may be suitably provided by a person who carries out theinvention.

FIG. 26D is a diagram showing an example of the structure of the lightsource optical system 2801 in FIG. 26C. In this embodiment, the lightsource optical system 2801 comprises a reflector 2811, a light source2812, lens arrays 2813, 2814, a polarization conversion element 2815,and a condenser lens 2816. The light source optical system shown in FIG.26D is merely an example, and is not particularly limited to theillustrated structure. For example, a person who carries out theinvention is allowed to suitably add to the light source optical systeman optical system such as an optical lens, a film having a polarizationfunction, a film for adjusting a phase difference, and an IR film.

Note that a transmission electro-optical device is used as the projectorshown in FIG. 26, a reflection type electro-optical device is notillustrated.

FIG. 27A is a portable telephone, and it includes a main body 2901, anaudio output section 2902, an audio input section 2903, a displayportion 2904, operation switches 2905, and an antenna 2906. The presentinvention can be applied to the display portion 2904.

FIG. 27B is a portable book (electronic book), and it includes a mainbody 3001, display portions 3002 and 3003, a recording medium 3004,operation switches 3005, and an antenna 3006. The present invention canbe applied to the display portions 3002 and 3003.

FIG. 27C is a display, and it includes a main body 3101, a support stand3102, and a display portion 3103. The present invention can be appliedto the display portion 3103. The display of the present invention isadvantageous for a large size screen in particular, and is advantageousfor a display equal to or greater than 10 inches (especially equal to orgreater than 30 inches) in diagonal.

The applicable range of the present invention is thus extremely wide,and it is possible to apply the present invention to electronicequipment in all fields. Further, the electronic equipment of Embodiment3 can be realized by using a constitution of any combination ofEmbodiments 1 and 2.

As has been described hereinbefore, according to the present invention,the orientation failures of the liquid crystal such as the disclinationor optical leakage of the liquid crystal display device when the blacklevel is displayed can be reduced to provide a liquid crystal displaydevice which has a high contrast and an excellent visibility.

When the adjoining pixel electrodes have the different polarities, asshown in a sectional view in FIG. 29, equipotential lines 903 curve atthe end portions of the pixel electrode 901 a and the pixel electrode901 b. The opposed electrode 902 is at 0 V (FIG. 29A). If the pixelelectrodes 901 a and 901 b are provided below their first end portionswith ridges 904, equipotential lines are formed along the pixelelectrodes so that their curvatures are suppressed at the end portionsof the pixel electrodes (FIG. 29B). As the overlap widths 905 of thepixel electrodes and the ridges are enlarged, even the equipotentiallines intrinsically parallel to the pixel electrode faces will curve(FIG. 29C). Accordingly, the optical leakage and the disclinationincrease. When the adjoining pixel electrodes are different inpolarities, therefore, the ridges below the first end portions of thepixel electrodes are preferably formed to optimize the overlap widthsbetween the pixel electrodes and the ridges.

When the adjoining pixel electrodes have the identical polarity, asshown in a sectional view of FIG. 28, the equipotential lines 903 curveat the end portions of the pixel electrode 901 a and the pixel electrode901 b, but the curving degrees are small (FIG. 28A). Therefore, theridges 904 formed below the end portions of the pixel electrodes willincrease the curvatures of the equipotential lines to cause adverseeffects (FIG. 28B).

The present invention makes use of this principle to prevent thecurvatures of the equipotential lines at the end portions of the pixelelectrodes thereby to increase the electric field normal to the surfaceof the opposed electrode and to reduce the disclination and the opticalleakage.

1. A liquid crystal display device comprising: a scanning line over asubstrate; a signal line intersecting the scanning line over thesubstrate; a pixel electrode electrically connected to the scanning lineand the signal line over the substrate; and an opposed electrode overthe pixel electrode, wherein the pixel electrode contains a main face, afirst face closer to the opposed electrode than the main face, and asecond face closer to the opposed electrode than the first face, whereinthe first face is extended along the scanning line, and wherein thesecond face is adjacent to an intersection between the scanning line andthe signal line.
 2. A liquid crystal display device according to claim1, wherein the liquid crystal display device is driven by a gate lineinversion drive.
 3. A liquid crystal display device according to claim1, wherein the liquid crystal display device is incorporated in oneselected from the group consisting of a personal computer, a videocamera, a mobile computer, a goggle type display, a DVD player, adigital camera, a projector, a portable telephone, and a portableelectronic book.
 4. A liquid crystal display device comprising: aplurality of pixel electrodes over a substrate, each of the plurality ofpixel electrodes containing a main face, and first to fourth endportions enclosing the main face, wherein the first end portion isextended along a first scanning line, and the third end portion isextended along a second scanning line adjacent to the first scanningline, and wherein the second end portion is extended along a firstsignal line and interposed between the first end portion and the thirdend portion, and the fourth end portion is extended along a secondsignal line adjacent to the first signal line and interposed between thefirst end portion and the third end portion; and an opposed electrodeover the plurality of pixel electrodes, wherein the second end portionand the fourth end portion are at a same height as the main face, andthe first end portion and the third end portion are disposed closer tothe opposed electrode than the main face, wherein two end portions ofthe first end portion are further closer to the opposed electrode thanthe center of the first end portion, and wherein two end portions of thethird end portion are further closer to the opposed electrode than thecenter of the third end portion.
 5. A liquid crystal display deviceaccording to claim 4, wherein the liquid crystal display device isdriven by a gate line inversion drive.
 6. A liquid crystal displaydevice according to claim 4, wherein the plurality of pixel electrodesare adjacent to each other such that a distance between the second endportion of one pixel electrode and the fourth end portion of the otherpixel electrode is 2.0 μm or less.
 7. A liquid crystal display deviceaccording to claim 4, wherein the two end portions of the first endportion are closer by 0.5 μm or more to the opposed electrode than thecentral portion of the first end portion.
 8. A liquid crystal displaydevice according to claim 4, wherein the two end portions of the thirdend portion are closer by 0.5 μm or more to the opposed electrode thanthe central portion of the third end portion.
 9. A liquid crystaldisplay device according to claim 4, wherein the liquid crystal displaydevice is incorporated in one selected from the group consisting of apersonal computer, a video camera, a mobile computer, a goggle typedisplay, a DVD player, a digital camera, a projector, a portabletelephone, and a portable electronic book.
 10. A liquid crystal displaydevice comprising: a scanning line over a substrate; a signal lineintersecting the scanning line over the substrate; a pixel electrodeelectrically connected to the scanning line and the signal line over thesubstrate; and an opposed electrode over the pixel electrode, whereinthe pixel electrode contains a main face, a first face closer to theopposed electrode than the main face, and a second face closer to theopposed electrode than the first face, wherein the first face isextended along the signal line, and wherein the second face is adjacentto an intersection between the scanning line and the signal line.
 11. Aliquid crystal display device according to claim 11, wherein the liquidcrystal display device is driven by a source line inversion drive.
 12. Aliquid crystal display device according to claim 11, wherein the liquidcrystal display device is incorporated in one selected from the groupconsisting of a personal computer, a video camera, a mobile computer, agoggle type display, a DVD player, a digital camera, a projector, aportable telephone, and a portable electronic book.
 13. A liquid crystaldisplay device comprising: a plurality of pixel electrodes over asubstrate, each of the plurality of pixel electrodes containing a mainface, and first to fourth end portions enclosing the main face, whereinthe first end portion is extended along a first signal line, and thethird end portion is extended along a second signal line adjacent to thefirst signal line, and wherein the second end portion is extended alonga first scanning line and interposed between the first end portion andthe third end portion, and the fourth end portion is extended along asecond scanning line adjacent to the first scanning line and interposedbetween the first end portion and the third end portion; and an opposedelectrode over the plurality of pixel electrodes, wherein the second endportion and the fourth end portion are at a same height as the mainface, and the first end portion and the third end portion are disposedcloser to the opposed electrode than the main face, wherein two endportions of the first end portion are further closer to the opposedelectrode than the center of the first end portion, and wherein two endportions of the third end portion are further closer to the opposedelectrode than the center of the third end portion.
 14. A liquid crystaldisplay device according to claim 14, wherein the liquid crystal displaydevice is driven by a source line inversion drive.
 15. A liquid crystaldisplay device according to claim 14, wherein the plurality of pixelelectrodes are adjacent to each other such that a distance between thesecond end portion of one pixel electrode and the fourth end portion ofthe other pixel electrode is 2.0 μm or less.
 16. A liquid crystaldisplay device according to claim 14, wherein the two end.-portions ofthe first end portion are closer by 0.5 μm or more to the opposedelectrode than the central portion of the first end portion.
 17. Aliquid crystal display device according to claim 14, wherein the two endportions of the third end portion are closer by 0.5 μm or more to theopposed electrode than the central portion of the third end portion. 18.A liquid crystal display device according to claim 14, wherein theliquid crystal display device is incorporated in one selected from thegroup consisting of a personal computer, a video camera, a mobilecomputer, a goggle type display, a DVD player, a digital camera, aprojector, a portable telephone, and a portable electronic book.
 19. Aliquid crystal display device comprising: a scanning line over asubstrate; a signal line intersecting the scanning line over thesubstrate; a pixel electrode electrically connected to the scanning lineand the signal line over the substrate; and an opposed electrode overthe pixel electrode, wherein the pixel electrode contains a main face,and a first face closer to the opposed electrode than the main face, andwherein the first face is extended along the scanning line.
 20. A liquidcrystal display device according to claim 20, wherein the liquid crystaldisplay device is driven by a gate line inversion drive.
 21. A liquidcrystal display device according to claim 20, wherein the liquid crystaldisplay device is incorporated in one selected from the group consistingof a personal computer, a video camera, a mobile computer, a goggle typedisplay, a DVD player, a digital camera, a projector, a portabletelephone, and a portable electronic book.
 22. A liquid crystal displaydevice comprising: a scanning line over a substrate; a signal lineintersecting the scanning line over the substrate; a pixel electrodeelectrically connected to the scanning line and the signal line over thesubstrate; and an opposed electrode over the pixel electrode, whereinthe pixel electrode contains a main face, and a first face closer to theopposed electrode than the main face, and wherein the first face isextended along the signal line.
 23. A liquid crystal display deviceaccording to claim 23, wherein the liquid crystal display device isdriven by a source line inversion drive.
 24. A liquid crystal displaydevice according to claim 23, wherein the liquid crystal display deviceis incorporated in one selected from the group consisting of a personalcomputer, a video camera, a mobile computer, a goggle type display, aDVD player, a digital camera, a projector, a portable telephone, and aportable electronic book.